1. Field of the Invention
The present invention relates to a communication system. Such a communication system can be a cellular or cordless telephony system, or any other suitable system. The system can be a terrestrial and/or satellite cellular mobile radio system in which the one radio station can be a radio base station in a terrestrial network or a mobile terminal, and the other radio station can be a satellite. The system can be an analog or digital system. In the event of a digital system, the system can be a so-called FD/TDMA-system (Frequency Division/Time Division Multiple Access), a CDMA-system (Code Division Multiple Access), or a mixed FD/TDMA- and CDMA-system, or any other suitable system.
The present invention further relates to a primary and a secondary radio station and a radio communication method for use in such a communication system.
2. Description of the Related Art
A communication system of the above kind is known from the handbook "Mobile Antenna Systems Handbook", K. Fujimoto et al., Artech House, Inc., 1994, pp. 436-451. The known system is a land mobile satellite communications system in which the primary radio stations are satellites and the secondary radio stations are mobile radio station in a vehicle. The secondary radio stations comprise a phased-array antenna as a controllable antenna structure. At pages 438-441 a satellite tracking method is described. The phased-array antenna is controlled on the basis of sensing information acquired by an optical-fibre gyro and a geomagnetic sensor, the sensing information being used in an open-loop control method. As is described on page 441, the geomagnetic sensor is used for sensing an absolute direction to calibrate the cumulative angular error of the optical-fibre gyro which can only sense relative directional variations. Optical-fibre gyros are relatively expensive or to slow to follow quick movements. Furthermore, measuring the absolute direction of the earth magnetic field is subject to static and dynamic magnetic field disturbances caused by the vehicle passing large buildings containing metal, inter alia. Also, since the earth magnetic field varies in a compicated way with geograpic position, sophisticated correction methods are needed, often requiring expensive additional sensors. It is at least difficult or even not feasible to implement the known method in a portable radio station such as a cellular radio handset which can be freely and rapidly oriented in different positions with respect to a fixed coordinate system.